This invention relates to apparatus for applying to a surface of a support member at least five ribbon-like streams of two different coating composition to form at least five adjacent edge to edge coating layers on the surface of a support member and process for using the apparatus.
Numerous techniques have been devised to form a layer of a coating composition on a substrate. One of these techniques involves the use of an extrusion die from which the coating composition is extruded onto the substrate. For fabrication of web type, flexible electrophotographic imaging members, the extrusion die must lay down very thin coatings meeting extremely precise, critical tolerances in the single or double digit micrometer ranges. Moreover, a plurality of dies may be needed to lay down up to three sequentially extruded coatings conventionally employed for flexible electrophotographic imaging members. The flexible electrophotographic imaging members may also comprise additional coatings applied by non-extrusion coating techniques so that the finished electrophotographic imaging member can contain as many as 4 sequentially applied different coating layers, one of the coating layers can comprising two different coating compositions applied edge to edge.
The extrusion die usually comprises spaced walls, each having a surface facing each other. These spaced walls form a narrow, elongated, passageway. Generally a coating composition is supplied by a reservoir to one side of the passageway and the coating composition travels through the passageway to an exit slot on the side of the passageway opposite the reservoir. The surface of the dams facing the coating composition is generally perpendicular to the exit slot. Dams or side walls are provided at opposite ends of the passageway to confine the coating composition within the passageway as the coating travels from the reservoir to the exit slot. Each end dam or side wall seals one end of the die. A second mini extrusion die may be bolted or otherwise attached to one end of the first extrusion die to share one of the dams of the first extrusion die so that one side of the dam forms one wall of the passageway in the first extrusion die and the other side of the dam forms a wall of the passageway in the second mini extrusion die. This permits the extrusion of an electrically conductive ground strip from the second die edge to edge with the wider charge transport layer coating material extruded from the first main die. Since flexible electrophotographic imaging members usually comprise an electrically conductive ground strip on one edge, this arrangement of extrusion dies is ideal for a fabrication lane which forms a photoreceptor in web form with a narrow electrically conductive ground strip layer along one edge of a charge transport layer. This technique is described in U.S. Pat. No 4,521,457, the entire disclosure thereof being incorporated herein by reference. The photoreceptor web is subsequently sliced transversely to form a rectangular sheet. The rectangular sheet is formed into a belt type photoreceptor by welding opposite ends of the sheet together.
The formation of a photoreceptor in web form using a single extrusion lane is extremely inefficient. A more efficient technique involves bolting a third mini extrusion die on the end of the first extrusion die opposite the end supporting the second mini extrusion die and to lengthen the first die. This establishes dual extrusion lanes for simultaneously fabricating two side by side photoreceptors. Using this technique, and electrically conductive ground strip can be formed along each edge of the enlarged large middle charge transport coating layer formed by the first extrusion die. After all the coatings have been deposited and dried, the web formed using the dual extrusion lanes can be slit longitudinally along its centerline to form two separate photoreceptor webs, each web having an electrically conducting ground strip along one edge thereof and being mirror images of each other. Since there are no additional extrusion die ends available for mounting mini extrusion dies, the maximum number of photoreceptor extrusion lanes available is two. Throughput cannot be increased beyond two photoreceptor extrusion lanes with this type of extrusion die arrangement.